System for growth of large aluminum nitride single crystals with thermal-gradient control

Abstract

In various embodiments, non-zero thermal gradients are formed within a growth chamber both substantially parallel and substantially perpendicular to the growth direction during formation of semiconductor crystals, where the ratio of the two thermal gradients (parallel to perpendicular) is less than 10, by, e.g., arrangement of thermal shields outside of the growth chamber.

What is claimed is: 
     
       1. A crystal-growth system comprising:
 a growth chamber for the formation of a single-crystal semiconductor material via sublimation-recondensation therewithin along a growth direction; 
 solid source material disposed within the growth chamber at a bottom surface thereof; 
 disposed within the growth chamber and over and facing the solid source material, a seed crystal for nucleating the single-crystal semiconductor material thereon; 
 a plurality of thermal shields arranged in a vertical stack disposed over the growth chamber, wherein (i) each thermal shield defines an opening therethrough, and (ii) the openings in the thermal shields increase in size among the thermal shields in a direction toward the solid source material. 
 
     
     
       2. The system of  claim 1 , wherein at least two of the thermal shields have different thicknesses. 
     
     
       3. The system of  claim 1 , wherein a thickness of each of the thermal shields ranges from 0.125 mm to 0.5 mm. 
     
     
       4. The system of  claim 1 , wherein at least one of the thermal shields comprises a refractory material. 
     
     
       5. The system of  claim 1 , wherein at least one of the thermal shields comprises tungsten. 
     
     
       6. The system of  claim 1 , wherein the thermal shields are arranged with spacings therebetween, the spacings being equal to each other ±10%. 
     
     
       7. The system of  claim 1 , wherein spacings between at least two pairs of the thermal shields are different. 
     
     
       8. The system of  claim 1 , wherein a diameter of the seed crystal is greater than 25 mm. 
     
     
       9. The system of  claim 1 , wherein the seed crystal comprises aluminum nitride. 
     
     
       10. The system of  claim 1 , further comprising a lid disposed on and at least partially enclosing the growth chamber, wherein the seed crystal is disposed beneath the lid. 
     
     
       11. The system of  claim 10 , wherein a thickness of the lid is less than 0.5 mm. 
     
     
       12. The system of  claim 10 , wherein the lid comprises tungsten. 
     
     
       13. The system of  claim 1 , wherein the seed crystal comprises single-crystal aluminum nitride. 
     
     
       14. The system of  claim 1 , wherein the solid source material comprises polycrystalline aluminum nitride. 
     
     
       15. The system of  claim 1 , wherein the thermal shields are arranged to form, within the growth chamber, (i) a first non-zero thermal gradient in a direction substantially parallel to the growth direction and (ii) a second non-zero thermal gradient in a direction substantially perpendicular to the growth direction. 
     
     
       16. The system of  claim 15 , wherein a ratio of the first thermal gradient to the second thermal gradient is less than 10. 
     
     
       17. The system of  claim 15 , wherein the second thermal gradient is larger than 4° C./cm. 
     
     
       18. The system of  claim 15 , wherein the second thermal gradient is smaller than 85° C./cm. 
     
     
       19. The system of  claim 15 , wherein the ratio of the first thermal gradient to the second thermal gradient is greater than 1.2. 
     
     
       20. The system of  claim 15 , wherein the first thermal gradient is larger than 5° C./cm. 
     
     
       21. The system of  claim 15 , wherein the first thermal gradient is smaller than 100° C./cm. 
     
     
       22. The system of  claim 15 , wherein the ratio of the first thermal gradient to the second thermal gradient is less than 5.5. 
     
     
       23. The system of  claim 15 , wherein the ratio of the first thermal gradient to the second thermal gradient is less than 3. 
     
     
       24. The system of  claim 1 , wherein the growth chamber comprises at least one of tungsten, rhenium, tantalum, tantalum carbide, tantalum nitride, hafnium, or hafnium nitride.